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129 .\" ========================================================================
131 .IX Title ""<STANDARD INPUT>" 1"
132 .TH "<STANDARD INPUT>" 1 "2007-11-13" "perl v5.8.8" "User Contributed Perl Documentation"
134 libev \- a high performance full\-featured event loop written in C
136 .IX Header "SYNOPSIS"
141 .IX Header "DESCRIPTION"
142 Libev is an event loop: you register interest in certain events (such as a
143 file descriptor being readable or a timeout occuring), and it will manage
144 these event sources and provide your program with events.
146 To do this, it must take more or less complete control over your process
147 (or thread) by executing the \fIevent loop\fR handler, and will then
148 communicate events via a callback mechanism.
150 You register interest in certain events by registering so-called \fIevent
151 watchers\fR, which are relatively small C structures you initialise with the
152 details of the event, and then hand it over to libev by \fIstarting\fR the
155 .IX Header "FEATURES"
156 Libev supports select, poll, the linux-specific epoll and the bsd-specific
157 kqueue mechanisms for file descriptor events, relative timers, absolute
158 timers with customised rescheduling, signal events, process status change
159 events (related to \s-1SIGCHLD\s0), and event watchers dealing with the event
160 loop mechanism itself (idle, prepare and check watchers). It also is quite
161 fast (see this benchmark comparing
162 it to libevent for example).
164 .IX Header "CONVENTIONS"
165 Libev is very configurable. In this manual the default configuration
166 will be described, which supports multiple event loops. For more info
167 about various configuration options please have a look at the file
168 \&\fI\s-1README\s0.embed\fR in the libev distribution. If libev was configured without
169 support for multiple event loops, then all functions taking an initial
170 argument of name \f(CW\*(C`loop\*(C'\fR (which is always of type \f(CW\*(C`struct ev_loop *\*(C'\fR)
171 will not have this argument.
172 .SH "TIME REPRESENTATION"
173 .IX Header "TIME REPRESENTATION"
174 Libev represents time as a single floating point number, representing the
175 (fractional) number of seconds since the (\s-1POSIX\s0) epoch (somewhere near
176 the beginning of 1970, details are complicated, don't ask). This type is
177 called \f(CW\*(C`ev_tstamp\*(C'\fR, which is what you should use too. It usually aliases
178 to the double type in C.
179 .SH "GLOBAL FUNCTIONS"
180 .IX Header "GLOBAL FUNCTIONS"
181 These functions can be called anytime, even before initialising the
183 .IP "ev_tstamp ev_time ()" 4
184 .IX Item "ev_tstamp ev_time ()"
185 Returns the current time as libev would use it.
186 .IP "int ev_version_major ()" 4
187 .IX Item "int ev_version_major ()"
189 .IP "int ev_version_minor ()" 4
190 .IX Item "int ev_version_minor ()"
192 You can find out the major and minor version numbers of the library
193 you linked against by calling the functions \f(CW\*(C`ev_version_major\*(C'\fR and
194 \&\f(CW\*(C`ev_version_minor\*(C'\fR. If you want, you can compare against the global
195 symbols \f(CW\*(C`EV_VERSION_MAJOR\*(C'\fR and \f(CW\*(C`EV_VERSION_MINOR\*(C'\fR, which specify the
196 version of the library your program was compiled against.
198 Usually, it's a good idea to terminate if the major versions mismatch,
199 as this indicates an incompatible change. Minor versions are usually
200 compatible to older versions, so a larger minor version alone is usually
202 .IP "ev_set_allocator (void *(*cb)(void *ptr, long size))" 4
203 .IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size))"
204 Sets the allocation function to use (the prototype is similar to the
205 realloc C function, the semantics are identical). It is used to allocate
206 and free memory (no surprises here). If it returns zero when memory
207 needs to be allocated, the library might abort or take some potentially
208 destructive action. The default is your system realloc function.
210 You could override this function in high-availability programs to, say,
211 free some memory if it cannot allocate memory, to use a special allocator,
212 or even to sleep a while and retry until some memory is available.
213 .IP "ev_set_syserr_cb (void (*cb)(const char *msg));" 4
214 .IX Item "ev_set_syserr_cb (void (*cb)(const char *msg));"
215 Set the callback function to call on a retryable syscall error (such
216 as failed select, poll, epoll_wait). The message is a printable string
217 indicating the system call or subsystem causing the problem. If this
218 callback is set, then libev will expect it to remedy the sitution, no
219 matter what, when it returns. That is, libev will generally retry the
220 requested operation, or, if the condition doesn't go away, do bad stuff
222 .SH "FUNCTIONS CONTROLLING THE EVENT LOOP"
223 .IX Header "FUNCTIONS CONTROLLING THE EVENT LOOP"
224 An event loop is described by a \f(CW\*(C`struct ev_loop *\*(C'\fR. The library knows two
225 types of such loops, the \fIdefault\fR loop, which supports signals and child
226 events, and dynamically created loops which do not.
228 If you use threads, a common model is to run the default event loop
229 in your main thread (or in a separate thread) and for each thread you
230 create, you also create another event loop. Libev itself does no locking
231 whatsoever, so if you mix calls to the same event loop in different
232 threads, make sure you lock (this is usually a bad idea, though, even if
233 done correctly, because it's hideous and inefficient).
234 .IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4
235 .IX Item "struct ev_loop *ev_default_loop (unsigned int flags)"
236 This will initialise the default event loop if it hasn't been initialised
237 yet and return it. If the default loop could not be initialised, returns
238 false. If it already was initialised it simply returns it (and ignores the
241 If you don't know what event loop to use, use the one returned from this
244 The flags argument can be used to specify special behaviour or specific
245 backends to use, and is usually specified as 0 (or \s-1EVFLAG_AUTO\s0).
247 It supports the following flags:
249 .ie n .IP """EVFLAG_AUTO""" 4
250 .el .IP "\f(CWEVFLAG_AUTO\fR" 4
251 .IX Item "EVFLAG_AUTO"
252 The default flags value. Use this if you have no clue (it's the right
254 .ie n .IP """EVFLAG_NOENV""" 4
255 .el .IP "\f(CWEVFLAG_NOENV\fR" 4
256 .IX Item "EVFLAG_NOENV"
257 If this flag bit is ored into the flag value (or the program runs setuid
258 or setgid) then libev will \fInot\fR look at the environment variable
259 \&\f(CW\*(C`LIBEV_FLAGS\*(C'\fR. Otherwise (the default), this environment variable will
260 override the flags completely if it is found in the environment. This is
261 useful to try out specific backends to test their performance, or to work
263 .ie n .IP """EVMETHOD_SELECT"" (portable select backend)" 4
264 .el .IP "\f(CWEVMETHOD_SELECT\fR (portable select backend)" 4
265 .IX Item "EVMETHOD_SELECT (portable select backend)"
267 .ie n .IP """EVMETHOD_POLL"" (poll backend, available everywhere except on windows)" 4
268 .el .IP "\f(CWEVMETHOD_POLL\fR (poll backend, available everywhere except on windows)" 4
269 .IX Item "EVMETHOD_POLL (poll backend, available everywhere except on windows)"
270 .ie n .IP """EVMETHOD_EPOLL"" (linux only)" 4
271 .el .IP "\f(CWEVMETHOD_EPOLL\fR (linux only)" 4
272 .IX Item "EVMETHOD_EPOLL (linux only)"
273 .ie n .IP """EVMETHOD_KQUEUE"" (some bsds only)" 4
274 .el .IP "\f(CWEVMETHOD_KQUEUE\fR (some bsds only)" 4
275 .IX Item "EVMETHOD_KQUEUE (some bsds only)"
276 .ie n .IP """EVMETHOD_DEVPOLL"" (solaris 8 only)" 4
277 .el .IP "\f(CWEVMETHOD_DEVPOLL\fR (solaris 8 only)" 4
278 .IX Item "EVMETHOD_DEVPOLL (solaris 8 only)"
279 .ie n .IP """EVMETHOD_PORT"" (solaris 10 only)" 4
280 .el .IP "\f(CWEVMETHOD_PORT\fR (solaris 10 only)" 4
281 .IX Item "EVMETHOD_PORT (solaris 10 only)"
283 If one or more of these are ored into the flags value, then only these
284 backends will be tried (in the reverse order as given here). If one are
285 specified, any backend will do.
289 .IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4
290 .IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"
291 Similar to \f(CW\*(C`ev_default_loop\*(C'\fR, but always creates a new event loop that is
292 always distinct from the default loop. Unlike the default loop, it cannot
293 handle signal and child watchers, and attempts to do so will be greeted by
294 undefined behaviour (or a failed assertion if assertions are enabled).
295 .IP "ev_default_destroy ()" 4
296 .IX Item "ev_default_destroy ()"
297 Destroys the default loop again (frees all memory and kernel state
298 etc.). This stops all registered event watchers (by not touching them in
299 any way whatsoever, although you cannot rely on this :).
300 .IP "ev_loop_destroy (loop)" 4
301 .IX Item "ev_loop_destroy (loop)"
302 Like \f(CW\*(C`ev_default_destroy\*(C'\fR, but destroys an event loop created by an
303 earlier call to \f(CW\*(C`ev_loop_new\*(C'\fR.
304 .IP "ev_default_fork ()" 4
305 .IX Item "ev_default_fork ()"
306 This function reinitialises the kernel state for backends that have
307 one. Despite the name, you can call it anytime, but it makes most sense
308 after forking, in either the parent or child process (or both, but that
309 again makes little sense).
311 You \fImust\fR call this function after forking if and only if you want to
312 use the event library in both processes. If you just fork+exec, you don't
315 The function itself is quite fast and it's usually not a problem to call
316 it just in case after a fork. To make this easy, the function will fit in
317 quite nicely into a call to \f(CW\*(C`pthread_atfork\*(C'\fR:
320 \& pthread_atfork (0, 0, ev_default_fork);
322 .IP "ev_loop_fork (loop)" 4
323 .IX Item "ev_loop_fork (loop)"
324 Like \f(CW\*(C`ev_default_fork\*(C'\fR, but acts on an event loop created by
325 \&\f(CW\*(C`ev_loop_new\*(C'\fR. Yes, you have to call this on every allocated event loop
326 after fork, and how you do this is entirely your own problem.
327 .IP "unsigned int ev_method (loop)" 4
328 .IX Item "unsigned int ev_method (loop)"
329 Returns one of the \f(CW\*(C`EVMETHOD_*\*(C'\fR flags indicating the event backend in
331 .IP "ev_tstamp ev_now (loop)" 4
332 .IX Item "ev_tstamp ev_now (loop)"
333 Returns the current \*(L"event loop time\*(R", which is the time the event loop
334 got events and started processing them. This timestamp does not change
335 as long as callbacks are being processed, and this is also the base time
336 used for relative timers. You can treat it as the timestamp of the event
337 occuring (or more correctly, the mainloop finding out about it).
338 .IP "ev_loop (loop, int flags)" 4
339 .IX Item "ev_loop (loop, int flags)"
340 Finally, this is it, the event handler. This function usually is called
341 after you initialised all your watchers and you want to start handling
344 If the flags argument is specified as 0, it will not return until either
345 no event watchers are active anymore or \f(CW\*(C`ev_unloop\*(C'\fR was called.
347 A flags value of \f(CW\*(C`EVLOOP_NONBLOCK\*(C'\fR will look for new events, will handle
348 those events and any outstanding ones, but will not block your process in
349 case there are no events and will return after one iteration of the loop.
351 A flags value of \f(CW\*(C`EVLOOP_ONESHOT\*(C'\fR will look for new events (waiting if
352 neccessary) and will handle those and any outstanding ones. It will block
353 your process until at least one new event arrives, and will return after
354 one iteration of the loop.
356 This flags value could be used to implement alternative looping
357 constructs, but the \f(CW\*(C`prepare\*(C'\fR and \f(CW\*(C`check\*(C'\fR watchers provide a better and
358 more generic mechanism.
359 .IP "ev_unloop (loop, how)" 4
360 .IX Item "ev_unloop (loop, how)"
361 Can be used to make a call to \f(CW\*(C`ev_loop\*(C'\fR return early (but only after it
362 has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either
363 \&\f(CW\*(C`EVUNLOOP_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_loop\*(C'\fR call return, or
364 \&\f(CW\*(C`EVUNLOOP_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_loop\*(C'\fR calls return.
365 .IP "ev_ref (loop)" 4
366 .IX Item "ev_ref (loop)"
368 .IP "ev_unref (loop)" 4
369 .IX Item "ev_unref (loop)"
371 Ref/unref can be used to add or remove a reference count on the event
372 loop: Every watcher keeps one reference, and as long as the reference
373 count is nonzero, \f(CW\*(C`ev_loop\*(C'\fR will not return on its own. If you have
374 a watcher you never unregister that should not keep \f(CW\*(C`ev_loop\*(C'\fR from
375 returning, \fIev_unref()\fR after starting, and \fIev_ref()\fR before stopping it. For
376 example, libev itself uses this for its internal signal pipe: It is not
377 visible to the libev user and should not keep \f(CW\*(C`ev_loop\*(C'\fR from exiting if
378 no event watchers registered by it are active. It is also an excellent
379 way to do this for generic recurring timers or from within third-party
380 libraries. Just remember to \fIunref after start\fR and \fIref before stop\fR.
381 .SH "ANATOMY OF A WATCHER"
382 .IX Header "ANATOMY OF A WATCHER"
383 A watcher is a structure that you create and register to record your
384 interest in some event. For instance, if you want to wait for \s-1STDIN\s0 to
385 become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher for that:
388 \& static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)
391 \& ev_unloop (loop, EVUNLOOP_ALL);
396 \& struct ev_loop *loop = ev_default_loop (0);
397 \& struct ev_io stdin_watcher;
398 \& ev_init (&stdin_watcher, my_cb);
399 \& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
400 \& ev_io_start (loop, &stdin_watcher);
401 \& ev_loop (loop, 0);
404 As you can see, you are responsible for allocating the memory for your
405 watcher structures (and it is usually a bad idea to do this on the stack,
406 although this can sometimes be quite valid).
408 Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init
409 (watcher *, callback)\*(C'\fR, which expects a callback to be provided. This
410 callback gets invoked each time the event occurs (or, in the case of io
411 watchers, each time the event loop detects that the file descriptor given
412 is readable and/or writable).
414 Each watcher type has its own \f(CW\*(C`ev_<type>_set (watcher *, ...)\*(C'\fR macro
415 with arguments specific to this watcher type. There is also a macro
416 to combine initialisation and setting in one call: \f(CW\*(C`ev_<type>_init
417 (watcher *, callback, ...)\*(C'\fR.
419 To make the watcher actually watch out for events, you have to start it
420 with a watcher-specific start function (\f(CW\*(C`ev_<type>_start (loop, watcher
421 *)\*(C'\fR), and you can stop watching for events at any time by calling the
422 corresponding stop function (\f(CW\*(C`ev_<type>_stop (loop, watcher *)\*(C'\fR.
424 As long as your watcher is active (has been started but not stopped) you
425 must not touch the values stored in it. Most specifically you must never
426 reinitialise it or call its set method.
428 You can check whether an event is active by calling the \f(CW\*(C`ev_is_active
429 (watcher *)\*(C'\fR macro. To see whether an event is outstanding (but the
430 callback for it has not been called yet) you can use the \f(CW\*(C`ev_is_pending
431 (watcher *)\*(C'\fR macro.
433 Each and every callback receives the event loop pointer as first, the
434 registered watcher structure as second, and a bitset of received events as
437 The received events usually include a single bit per event type received
438 (you can receive multiple events at the same time). The possible bit masks
440 .ie n .IP """EV_READ""" 4
441 .el .IP "\f(CWEV_READ\fR" 4
444 .ie n .IP """EV_WRITE""" 4
445 .el .IP "\f(CWEV_WRITE\fR" 4
448 The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or
450 .ie n .IP """EV_TIMEOUT""" 4
451 .el .IP "\f(CWEV_TIMEOUT\fR" 4
452 .IX Item "EV_TIMEOUT"
453 The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out.
454 .ie n .IP """EV_PERIODIC""" 4
455 .el .IP "\f(CWEV_PERIODIC\fR" 4
456 .IX Item "EV_PERIODIC"
457 The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out.
458 .ie n .IP """EV_SIGNAL""" 4
459 .el .IP "\f(CWEV_SIGNAL\fR" 4
461 The signal specified in the \f(CW\*(C`ev_signal\*(C'\fR watcher has been received by a thread.
462 .ie n .IP """EV_CHILD""" 4
463 .el .IP "\f(CWEV_CHILD\fR" 4
465 The pid specified in the \f(CW\*(C`ev_child\*(C'\fR watcher has received a status change.
466 .ie n .IP """EV_IDLE""" 4
467 .el .IP "\f(CWEV_IDLE\fR" 4
469 The \f(CW\*(C`ev_idle\*(C'\fR watcher has determined that you have nothing better to do.
470 .ie n .IP """EV_PREPARE""" 4
471 .el .IP "\f(CWEV_PREPARE\fR" 4
472 .IX Item "EV_PREPARE"
474 .ie n .IP """EV_CHECK""" 4
475 .el .IP "\f(CWEV_CHECK\fR" 4
478 All \f(CW\*(C`ev_prepare\*(C'\fR watchers are invoked just \fIbefore\fR \f(CW\*(C`ev_loop\*(C'\fR starts
479 to gather new events, and all \f(CW\*(C`ev_check\*(C'\fR watchers are invoked just after
480 \&\f(CW\*(C`ev_loop\*(C'\fR has gathered them, but before it invokes any callbacks for any
481 received events. Callbacks of both watcher types can start and stop as
482 many watchers as they want, and all of them will be taken into account
483 (for example, a \f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep
484 \&\f(CW\*(C`ev_loop\*(C'\fR from blocking).
485 .ie n .IP """EV_ERROR""" 4
486 .el .IP "\f(CWEV_ERROR\fR" 4
488 An unspecified error has occured, the watcher has been stopped. This might
489 happen because the watcher could not be properly started because libev
490 ran out of memory, a file descriptor was found to be closed or any other
491 problem. You best act on it by reporting the problem and somehow coping
492 with the watcher being stopped.
494 Libev will usually signal a few \*(L"dummy\*(R" events together with an error,
495 for example it might indicate that a fd is readable or writable, and if
496 your callbacks is well-written it can just attempt the operation and cope
497 with the error from \fIread()\fR or \fIwrite()\fR. This will not work in multithreaded
498 programs, though, so beware.
499 .Sh "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0"
500 .IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER"
501 Each watcher has, by default, a member \f(CW\*(C`void *data\*(C'\fR that you can change
502 and read at any time, libev will completely ignore it. This can be used
503 to associate arbitrary data with your watcher. If you need more data and
504 don't want to allocate memory and store a pointer to it in that data
505 member, you can also \*(L"subclass\*(R" the watcher type and provide your own
514 \& struct whatever *mostinteresting;
518 And since your callback will be called with a pointer to the watcher, you
519 can cast it back to your own type:
522 \& static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
524 \& struct my_io *w = (struct my_io *)w_;
529 More interesting and less C\-conformant ways of catsing your callback type
530 have been omitted....
532 .IX Header "WATCHER TYPES"
533 This section describes each watcher in detail, but will not repeat
534 information given in the last section.
535 .ie n .Sh """ev_io"" \- is this file descriptor readable or writable"
536 .el .Sh "\f(CWev_io\fP \- is this file descriptor readable or writable"
537 .IX Subsection "ev_io - is this file descriptor readable or writable"
538 I/O watchers check whether a file descriptor is readable or writable
539 in each iteration of the event loop (This behaviour is called
540 level-triggering because you keep receiving events as long as the
541 condition persists. Remember you can stop the watcher if you don't want to
542 act on the event and neither want to receive future events).
544 In general you can register as many read and/or write event watchers per
545 fd as you want (as long as you don't confuse yourself). Setting all file
546 descriptors to non-blocking mode is also usually a good idea (but not
547 required if you know what you are doing).
549 You have to be careful with dup'ed file descriptors, though. Some backends
550 (the linux epoll backend is a notable example) cannot handle dup'ed file
551 descriptors correctly if you register interest in two or more fds pointing
552 to the same underlying file/socket etc. description (that is, they share
553 the same underlying \*(L"file open\*(R").
555 If you must do this, then force the use of a known-to-be-good backend
556 (at the time of this writing, this includes only \s-1EVMETHOD_SELECT\s0 and
557 \&\s-1EVMETHOD_POLL\s0).
558 .IP "ev_io_init (ev_io *, callback, int fd, int events)" 4
559 .IX Item "ev_io_init (ev_io *, callback, int fd, int events)"
561 .IP "ev_io_set (ev_io *, int fd, int events)" 4
562 .IX Item "ev_io_set (ev_io *, int fd, int events)"
564 Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The fd is the file descriptor to rceeive
565 events for and events is either \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or \f(CW\*(C`EV_READ |
566 EV_WRITE\*(C'\fR to receive the given events.
567 .ie n .Sh """ev_timer"" \- relative and optionally recurring timeouts"
568 .el .Sh "\f(CWev_timer\fP \- relative and optionally recurring timeouts"
569 .IX Subsection "ev_timer - relative and optionally recurring timeouts"
570 Timer watchers are simple relative timers that generate an event after a
571 given time, and optionally repeating in regular intervals after that.
573 The timers are based on real time, that is, if you register an event that
574 times out after an hour and you reset your system clock to last years
575 time, it will still time out after (roughly) and hour. \*(L"Roughly\*(R" because
576 detecting time jumps is hard, and soem inaccuracies are unavoidable (the
577 monotonic clock option helps a lot here).
579 The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR
580 time. This is usually the right thing as this timestamp refers to the time
581 of the event triggering whatever timeout you are modifying/starting. If
582 you suspect event processing to be delayed and you *need* to base the timeout
583 on the current time, use something like this to adjust for this:
586 \& ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
588 .IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4
589 .IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)"
591 .IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4
592 .IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)"
594 Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR is
595 \&\f(CW0.\fR, then it will automatically be stopped. If it is positive, then the
596 timer will automatically be configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds
597 later, again, and again, until stopped manually.
599 The timer itself will do a best-effort at avoiding drift, that is, if you
600 configure a timer to trigger every 10 seconds, then it will trigger at
601 exactly 10 second intervals. If, however, your program cannot keep up with
602 the timer (because it takes longer than those 10 seconds to do stuff) the
603 timer will not fire more than once per event loop iteration.
604 .IP "ev_timer_again (loop)" 4
605 .IX Item "ev_timer_again (loop)"
606 This will act as if the timer timed out and restart it again if it is
607 repeating. The exact semantics are:
609 If the timer is started but nonrepeating, stop it.
611 If the timer is repeating, either start it if necessary (with the repeat
612 value), or reset the running timer to the repeat value.
614 This sounds a bit complicated, but here is a useful and typical
615 example: Imagine you have a tcp connection and you want a so-called idle
616 timeout, that is, you want to be called when there have been, say, 60
617 seconds of inactivity on the socket. The easiest way to do this is to
618 configure an \f(CW\*(C`ev_timer\*(C'\fR with after=repeat=60 and calling ev_timer_again each
619 time you successfully read or write some data. If you go into an idle
620 state where you do not expect data to travel on the socket, you can stop
621 the timer, and again will automatically restart it if need be.
622 .ie n .Sh """ev_periodic"" \- to cron or not to cron"
623 .el .Sh "\f(CWev_periodic\fP \- to cron or not to cron"
624 .IX Subsection "ev_periodic - to cron or not to cron"
625 Periodic watchers are also timers of a kind, but they are very versatile
626 (and unfortunately a bit complex).
628 Unlike \f(CW\*(C`ev_timer\*(C'\fR's, they are not based on real time (or relative time)
629 but on wallclock time (absolute time). You can tell a periodic watcher
630 to trigger \*(L"at\*(R" some specific point in time. For example, if you tell a
631 periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now ()
632 + 10.>) and then reset your system clock to the last year, then it will
633 take a year to trigger the event (unlike an \f(CW\*(C`ev_timer\*(C'\fR, which would trigger
634 roughly 10 seconds later and of course not if you reset your system time
637 They can also be used to implement vastly more complex timers, such as
638 triggering an event on eahc midnight, local time.
639 .IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 4
640 .IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)"
642 .IP "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 4
643 .IX Item "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)"
645 Lots of arguments, lets sort it out... There are basically three modes of
646 operation, and we will explain them from simplest to complex:
648 .IP "* absolute timer (interval = reschedule_cb = 0)" 4
649 .IX Item "absolute timer (interval = reschedule_cb = 0)"
650 In this configuration the watcher triggers an event at the wallclock time
651 \&\f(CW\*(C`at\*(C'\fR and doesn't repeat. It will not adjust when a time jump occurs,
652 that is, if it is to be run at January 1st 2011 then it will run when the
653 system time reaches or surpasses this time.
654 .IP "* non-repeating interval timer (interval > 0, reschedule_cb = 0)" 4
655 .IX Item "non-repeating interval timer (interval > 0, reschedule_cb = 0)"
656 In this mode the watcher will always be scheduled to time out at the next
657 \&\f(CW\*(C`at + N * interval\*(C'\fR time (for some integer N) and then repeat, regardless
660 This can be used to create timers that do not drift with respect to system
664 \& ev_periodic_set (&periodic, 0., 3600., 0);
667 This doesn't mean there will always be 3600 seconds in between triggers,
668 but only that the the callback will be called when the system time shows a
669 full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible
672 Another way to think about it (for the mathematically inclined) is that
673 \&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible
674 time where \f(CW\*(C`time = at (mod interval)\*(C'\fR, regardless of any time jumps.
675 .IP "* manual reschedule mode (reschedule_cb = callback)" 4
676 .IX Item "manual reschedule mode (reschedule_cb = callback)"
677 In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`at\*(C'\fR are both being
678 ignored. Instead, each time the periodic watcher gets scheduled, the
679 reschedule callback will be called with the watcher as first, and the
680 current time as second argument.
682 \&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher,
683 ever, or make any event loop modifications\fR. If you need to stop it,
684 return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop it afterwards (e.g. by
685 starting a prepare watcher).
687 Its prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
688 ev_tstamp now)\*(C'\fR, e.g.:
691 \& static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
697 It must return the next time to trigger, based on the passed time value
698 (that is, the lowest time value larger than to the second argument). It
699 will usually be called just before the callback will be triggered, but
700 might be called at other times, too.
702 \&\s-1NOTE:\s0 \fIThis callback must always return a time that is later than the
703 passed \f(CI\*(C`now\*(C'\fI value\fR. Not even \f(CW\*(C`now\*(C'\fR itself will do, it \fImust\fR be larger.
705 This can be used to create very complex timers, such as a timer that
706 triggers on each midnight, local time. To do this, you would calculate the
707 next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How
708 you do this is, again, up to you (but it is not trivial, which is the main
709 reason I omitted it as an example).
713 .IP "ev_periodic_again (loop, ev_periodic *)" 4
714 .IX Item "ev_periodic_again (loop, ev_periodic *)"
715 Simply stops and restarts the periodic watcher again. This is only useful
716 when you changed some parameters or the reschedule callback would return
717 a different time than the last time it was called (e.g. in a crond like
718 program when the crontabs have changed).
719 .ie n .Sh """ev_signal"" \- signal me when a signal gets signalled"
720 .el .Sh "\f(CWev_signal\fP \- signal me when a signal gets signalled"
721 .IX Subsection "ev_signal - signal me when a signal gets signalled"
722 Signal watchers will trigger an event when the process receives a specific
723 signal one or more times. Even though signals are very asynchronous, libev
724 will try it's best to deliver signals synchronously, i.e. as part of the
725 normal event processing, like any other event.
727 You can configure as many watchers as you like per signal. Only when the
728 first watcher gets started will libev actually register a signal watcher
729 with the kernel (thus it coexists with your own signal handlers as long
730 as you don't register any with libev). Similarly, when the last signal
731 watcher for a signal is stopped libev will reset the signal handler to
732 \&\s-1SIG_DFL\s0 (regardless of what it was set to before).
733 .IP "ev_signal_init (ev_signal *, callback, int signum)" 4
734 .IX Item "ev_signal_init (ev_signal *, callback, int signum)"
736 .IP "ev_signal_set (ev_signal *, int signum)" 4
737 .IX Item "ev_signal_set (ev_signal *, int signum)"
739 Configures the watcher to trigger on the given signal number (usually one
740 of the \f(CW\*(C`SIGxxx\*(C'\fR constants).
741 .ie n .Sh """ev_child"" \- wait for pid status changes"
742 .el .Sh "\f(CWev_child\fP \- wait for pid status changes"
743 .IX Subsection "ev_child - wait for pid status changes"
744 Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to
745 some child status changes (most typically when a child of yours dies).
746 .IP "ev_child_init (ev_child *, callback, int pid)" 4
747 .IX Item "ev_child_init (ev_child *, callback, int pid)"
749 .IP "ev_child_set (ev_child *, int pid)" 4
750 .IX Item "ev_child_set (ev_child *, int pid)"
752 Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or
753 \&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look
754 at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see
755 the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems
756 \&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the
757 process causing the status change.
758 .ie n .Sh """ev_idle"" \- when you've got nothing better to do"
759 .el .Sh "\f(CWev_idle\fP \- when you've got nothing better to do"
760 .IX Subsection "ev_idle - when you've got nothing better to do"
761 Idle watchers trigger events when there are no other events are pending
762 (prepare, check and other idle watchers do not count). That is, as long
763 as your process is busy handling sockets or timeouts (or even signals,
764 imagine) it will not be triggered. But when your process is idle all idle
765 watchers are being called again and again, once per event loop iteration \-
766 until stopped, that is, or your process receives more events and becomes
769 The most noteworthy effect is that as long as any idle watchers are
770 active, the process will not block when waiting for new events.
772 Apart from keeping your process non-blocking (which is a useful
773 effect on its own sometimes), idle watchers are a good place to do
774 \&\*(L"pseudo\-background processing\*(R", or delay processing stuff to after the
775 event loop has handled all outstanding events.
776 .IP "ev_idle_init (ev_signal *, callback)" 4
777 .IX Item "ev_idle_init (ev_signal *, callback)"
778 Initialises and configures the idle watcher \- it has no parameters of any
779 kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless,
781 .ie n .Sh """ev_prepare""\fP and \f(CW""ev_check"" \- customise your event loop"
782 .el .Sh "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop"
783 .IX Subsection "ev_prepare and ev_check - customise your event loop"
784 Prepare and check watchers are usually (but not always) used in tandem:
785 prepare watchers get invoked before the process blocks and check watchers
788 Their main purpose is to integrate other event mechanisms into libev. This
789 could be used, for example, to track variable changes, implement your own
790 watchers, integrate net-snmp or a coroutine library and lots more.
792 This is done by examining in each prepare call which file descriptors need
793 to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers for
794 them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many libraries
795 provide just this functionality). Then, in the check watcher you check for
796 any events that occured (by checking the pending status of all watchers
797 and stopping them) and call back into the library. The I/O and timer
798 callbacks will never actually be called (but must be valid nevertheless,
799 because you never know, you know?).
801 As another example, the Perl Coro module uses these hooks to integrate
802 coroutines into libev programs, by yielding to other active coroutines
803 during each prepare and only letting the process block if no coroutines
804 are ready to run (it's actually more complicated: it only runs coroutines
805 with priority higher than or equal to the event loop and one coroutine
806 of lower priority, but only once, using idle watchers to keep the event
807 loop from blocking if lower-priority coroutines are active, thus mapping
808 low-priority coroutines to idle/background tasks).
809 .IP "ev_prepare_init (ev_prepare *, callback)" 4
810 .IX Item "ev_prepare_init (ev_prepare *, callback)"
812 .IP "ev_check_init (ev_check *, callback)" 4
813 .IX Item "ev_check_init (ev_check *, callback)"
815 Initialises and configures the prepare or check watcher \- they have no
816 parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR
817 macros, but using them is utterly, utterly and completely pointless.
818 .SH "OTHER FUNCTIONS"
819 .IX Header "OTHER FUNCTIONS"
820 There are some other functions of possible interest. Described. Here. Now.
821 .IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4
822 .IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)"
823 This function combines a simple timer and an I/O watcher, calls your
824 callback on whichever event happens first and automatically stop both
825 watchers. This is useful if you want to wait for a single event on an fd
826 or timeout without having to allocate/configure/start/stop/free one or
827 more watchers yourself.
829 If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and events
830 is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for the given \f(CW\*(C`fd\*(C'\fR and
831 \&\f(CW\*(C`events\*(C'\fR set will be craeted and started.
833 If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be
834 started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and
835 repeat = 0) will be started. While \f(CW0\fR is a valid timeout, it is of
838 The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and gets
839 passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of
840 \&\f(CW\*(C`EV_ERROR\*(C'\fR, \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or \f(CW\*(C`EV_TIMEOUT\*(C'\fR) and the \f(CW\*(C`arg\*(C'\fR
841 value passed to \f(CW\*(C`ev_once\*(C'\fR:
844 \& static void stdin_ready (int revents, void *arg)
846 \& if (revents & EV_TIMEOUT)
847 \& /* doh, nothing entered */;
848 \& else if (revents & EV_READ)
849 \& /* stdin might have data for us, joy! */;
854 \& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
856 .IP "ev_feed_event (loop, watcher, int events)" 4
857 .IX Item "ev_feed_event (loop, watcher, int events)"
858 Feeds the given event set into the event loop, as if the specified event
859 had happened for the specified watcher (which must be a pointer to an
860 initialised but not necessarily started event watcher).
861 .IP "ev_feed_fd_event (loop, int fd, int revents)" 4
862 .IX Item "ev_feed_fd_event (loop, int fd, int revents)"
863 Feed an event on the given fd, as if a file descriptor backend detected
865 .IP "ev_feed_signal_event (loop, int signum)" 4
866 .IX Item "ev_feed_signal_event (loop, int signum)"
867 Feed an event as if the given signal occured (loop must be the default loop!).
868 .SH "LIBEVENT EMULATION"
869 .IX Header "LIBEVENT EMULATION"
870 Libev offers a compatibility emulation layer for libevent. It cannot
871 emulate the internals of libevent, so here are some usage hints:
872 .IP "* Use it by including <event.h>, as usual." 4
873 .IX Item "Use it by including <event.h>, as usual."
875 .IP "* The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events." 4
876 .IX Item "The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events."
877 .IP "* Avoid using ev_flags and the EVLIST_*\-macros, while it is maintained by libev, it does not work exactly the same way as in libevent (consider it a private \s-1API\s0)." 4
878 .IX Item "Avoid using ev_flags and the EVLIST_*-macros, while it is maintained by libev, it does not work exactly the same way as in libevent (consider it a private API)."
879 .IP "* Priorities are not currently supported. Initialising priorities will fail and all watchers will have the same priority, even though there is an ev_pri field." 4
880 .IX Item "Priorities are not currently supported. Initialising priorities will fail and all watchers will have the same priority, even though there is an ev_pri field."
881 .IP "* Other members are not supported." 4
882 .IX Item "Other members are not supported."
883 .IP "* The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need to use the libev header file and library." 4
884 .IX Item "The libev emulation is not ABI compatible to libevent, you need to use the libev header file and library."
887 .IX Header " SUPPORT"
891 Marc Lehmann <libev@schmorp.de>.
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